1. Field
The present disclosure relates to a light driving apparatus, and more particularly, to a light driving apparatus which may stably drive an LED light.
2. Description of the Related Art
Recently, the interest on an LED light operated with low power consumption and having brightness comparable with a light device such as an incandescent lamp is increasing.
In particular, a light driving apparatus for controlling a constant current to flow through the LED light so as to operate the LED light is being actively studied and developed. The light driving apparatus has various light displaying functions, and such various light displays may be performed by changing dimming of LED elements arranged to connect in parallel.
FIG. 1 is a diagram a general light driving apparatus, and FIG. 2 is a diagram exemplarily showing an output voltage and an LED current format according to a dimming control signal of the general light driving apparatus.
Referring to FIGS. 1 and 2, the general light driving apparatus includes a rectifier circuit 110 for rectifying the full wave output from an AC power source 100, a transformer circuit 120 for changing the magnitude of the voltage output from the rectifier circuit 110 and outputting the voltage, a power factor correction circuit 130 for detecting a load size by using a feedback voltage, controlling the output voltage of the transformer circuit 120 according to the detected load size, and compensating a power factor of the power output from the AC power source 100, a smoothing circuit 140 for smoothing the voltage output from the transformer circuit 120 to output a stable DC voltage and supplying the output voltage VOUT to an LED module 10, a constant-current driving circuit 150 for controlling an LED current ILED so that a constant current flows through the LED module 10, a dimming control circuit 160 for controlling a current flow of the LED module 10 by means of a pulse width modulation (PWM) method to control dimming, and a photo-coupler 170 operated by the output voltage Vo of the LED module 10 transmitted through the constant-current driving circuit 150 and applying a feedback voltage to the power factor correction circuit 130.
The light driving apparatus is classified into a primary side and a secondary side based on the transformer circuit 120 and the photo-coupler 170. The primary side includes the AC power source 100, the rectifier circuit 110 and the power factor correction circuit 130, and the secondary side includes the LED module 10, the smoothing circuit 140, the constant-current driving circuit 150 and the dimming control circuit 160.
Here, the LED module 10 is configured so that LED electrodes are connected in series, and it may emit a single light or various lights, selectively.
In addition, the transformer circuit 120 is composed of a plurality of transformers TF1 and TF2. Here, the first transformer TF1 of the primary side functions to transmit the voltage output from the rectifier circuit 110 to the second transformer TF2 of the secondary side. In addition, the second transformer TF2 functions to convert the voltage transmitted from the first transformer TF1 and output the converted voltage.
The power factor correction circuit 130 includes a power factor compensation controller 132 for squaring a phase of the AC power source voltage output from the AC power source 100 with a phase of the AC input current IAC and compensating a power factor of the AC power source 100, and a switch element SW such as an MOSFET for switching according to the control of the power factor compensation controller 132 to adjust the output voltage of the transformer circuit 120.
The power factor compensation controller 132 receives a AC power source voltage distributed by predetermined resistances R1, R2, R3 to square phases of the AC power source voltage and the AC input current IAC, and adjusts the gate voltage VG of the switch element SW according to the load size of the LED module 10 to control a current capacity flowing through the switch element SW so that the output voltage of the transformer circuit 120 may be adjusted.
In other words, as a high voltage is applied to an input terminal OPTO of the photo-coupler 170 so that the photo-coupler 170 is operated by the high voltage, the power factor compensation controller 132 determines that a small load is applied to the LED module 10 and applies a low gate voltage VG to the switch element SW, so that the current capacity flowing through the switch element SW is lowered to decrease the output voltage of the transformer circuit 120. Meanwhile, as a low voltage is applied to the input terminal OPTO of the photo-coupler 170 so that the photo-coupler 170 is operated by the low voltage, the power factor compensation controller 132 determines that a heavy load is applied to the LED module 10 and applies a high gate voltage VG to the switch element SW, so that the current capacity flowing through the switch element SW rises to increase the output voltage of the transformer circuit 120.
The smoothing circuit 140 includes a predetermined capacitor connecting to the output terminal of the transformer circuit 120 in parallel.
The dimming control circuit 160 includes a first switch element SW1 switched to turn on/off according to a PWM signal PWM generated by a PWM controller to adjust the current flow of the LED module 10.
In the general light driving apparatus as described above, when controlling the dimming of the LED light, the range of fluctuation of the voltage magnitude of the input terminal OPTO of the photo-coupler 170 is very large and unstable according to the logic value of the PWM signal PWM. Therefore, as shown in FIG. 2, when the logic value of the PWM signal PWM is high, the output voltage VOUT of the light driving apparatus supplied to the LED module 10 rises up to an over voltage protection (OVP), and in the transition region of the logic value, an over-current occurs at the LED module 10 which shortens the life span of LED elements of the LED module 10.
In addition, in the general light driving apparatus, in the case where the LED module 10 is opened due to surge generation or external factors and thus is operated abnormally, as shown in FIG. 3, the LED current ILED substantially does not flow and the output voltage Vo of the LED module 10 is lowered to the low voltage. At this time, since the photo-coupler 170 is operated due to only the output voltage Vo of the LED module 10 to supply the feedback voltage to the power factor correction circuit 130, the situation where the LED current ILED does not flow through the power factor correction circuit 130 is determined as a heavy load is applied, and the output voltage of the transformer circuit 120, namely the voltage VOUT supplied to the LED module 10 is boosted to the saturation voltage, for example up to about 300V, thereby causing accidents such as damaging a circuit or breaking an element.